Among the characteristics of a Minimum Drive Test (MDT), an important aspect is how to obtain relatively precise location information. An existing scheme is as follows: a User Equipment (UE) tries its best to provide location information according to its own condition without additionally obtaining location information for the MDT.
If a UE is provided with the function of a Global Navigation Satellite System (GNSS), e.g., a Global Positioning System (GPS), then the current location of the UE can be obtained directly by using the GPS, which is referred to as standalone GNSS positioning.
Due to the costly GPS and considerable fading of a GPS signal in an indoor scenario, a scheme has been proposed to obtain location information of a UE over a mobile communication network, i.e., a LoCation Service (LCS), typically the Cell Identifier (ID) and enhanced Cell ID schemes, the Observed Time Difference of Arrival (OTDOA) scheme, the Assisted-Global Navigation Satellite System (A-GNSS) scheme, etc.
An LTE LCS control-plane positioning flow as illustrated in FIG. 1 includes the following steps:
1. A Mobility Management Entity (MME) receives a location service request, which may be a request initiated by a UE to the MME via a Non-Access Stratum message or may be a location service request initiated by some entity in an Evolved Packet Core (EPC) (e.g., a Gateway Mobile Location Center (GMLC)) or initiated inside the MME;
2. The MME sends the location service request to an Enhanced Serving Mobile Location Center (E-SMLC), and the E-SMLC selects an appropriate positioning scheme according to Quality of Service (QoS) information carried in the location service request, e.g., the precision and delay in positioning, etc.;
3a. The E-SMLC may trigger an eNB-related positioning procedure according to the LTE Positioning Protocol A (LPPa), for example, to obtain auxiliary data required for positioning or a measurement required for positioning;
3b. The E-SMLC may trigger a UE-related positioning procedure according to the LTE Positioning Protocol (LPP), for example, to obtain a location estimation, to transmit auxiliary data required for positioning or to obtain a measurement required for positioning;
4. The E-SMLC sends a location service response to the MME, which includes some required results, e.g., the location of the UE, an indicator of a successful positioning or a failed positioning, etc.;
5. The MME sends the location service response to the target entity.
Apparently, if the location information of the UE is obtained through the LCS positioning scheme, then the UE has to be in a connected state and interact with multiple network nodes.
A context of the TADV+AoA positioning scheme (an enhanced cell ID-based positioning scheme) will be introduced below.
The positioning principle is as follows:
In the cell ID-based positioning scheme which is a cell coverage-based positioning scheme, the location of a target UE is estimated from known geographical information of a serving cell. The geographical information of the serving cell can be obtained through calling, paging, Tracking Area (TA) updating, etc. In the TADV+AoA positioning scheme based on the cell ID-positioning scheme, the factors of a Timing Advance (TADV) and an Angle of Arrival (AoA) are taken into account for the purpose of more precise positioning.
An evolved Node B (eNB) obtains the AoA of the UE transmitting a signal via an intelligent antenna, where the UE lies on a radial line starting from the eNB and rotated counterclockwise from the direction of the exact north by the AoA;
The TADV can be derived from the time difference between UE reception and transmission, reported by the user equipment, plus the time difference between reception and transmission, measured by the eNB (the TADV calculated as such is referred to as a TADV TYPE1), or can be measured by the eNB during a dedicated random access procedure (the TADV calculated as such is referred to as a TADV TYPE2). A result that the TADV is multiplied with the velocity of light and then is divided by two represents the distance between the UE and the eNB, where the UE lies on a circle with the center thereof being the eNB and the radius being the distance between the user equipment and the eNB, and location information of the user equipment can be obtained according to the angle information of the AoA, as illustrated in FIG. 2.
The TADV+AoA positioning scheme is typically applicable to network-based positioning, primarily because the AoA can be measured only by the eNB, and the TADV TYPE1 and the TADV TYPE2 are also calculated or measured by the eNB, that is, all of the measured quantities related to the positioning scheme are provided by the eNB. All of these measured quantities can be provided by the eNB to a location server, so the purpose of positioning can be achieved by supporting network-based positioning. There is such a resulted advantage of the scheme that a user equipment for which no location service is supported can also be positioned through this scheme.
A positioning flow is as flows:
Positioning by using this scheme an existing LTE system generally relates to the following flow:
A measurement capability of a user equipment is obtained, a location server decides a required measured quantity, an eNB starts a relevant measurement, the eNB reports a relevant measurement result and location information, and the location server calculates about the location. General flows of the TADV+AoA positioning scheme in two scenarios will be given below:
In a first scenario, positioning is performed by using measurement results of TADV TYPE1+AoA, as illustrated in FIG. 3, this process includes the following steps:
Step 11: A UE initiates a location request to an MME via an NAS message to request for its own location information, or some LoCation Service (LCS) client may initiate a location request to the MME to request for location information of some UE;
Step 12: The MME initiates the location request to an E-SMLC;
Step 13a/13b: The E-SMLC inquires about and obtains positioning capability information of the UE;
Step 14a/14b/14c: The E-SMLC obtains a relevant measurement result of an eNB and information of a serving cell;
Step 15a/15b/15c: The eNB triggers measurements of a TADV TYPE1, a timing deviation for receiving a signal from the UE by the eNB, and the AoA as requested by the E-SMLC;
Step 16: The E-SMLC calculates location information of the UE according to measurement results of the eNB and inputs from other parts;
Step 17: The E-SMLC sends a location result (the location information) to the MME;
Step 18: The MME sends the location result (the location information) to the UE or the LoCation Service (LCS) client.
In a second scenario, positioning is performed by using measurement results of TADV TYPE2+AoA, as illustrated in FIG. 4, this process includes the following steps:
Step 21: Some LoCation Service (LCS) client initiates a location request to an MME to request for location information of some UE, which may be a user equipment supporting a location service or may be a user equipment supporting no location service;
Step 22: The MME initiates the location request to an E-SMLC;
Step 23a/23b: The E-SMLC inquires about and obtains positioning capability information of the UE, where this step may be skipped if the UE supports no location service;
Step 24a/24b/24c: The E-SMLC obtains a relevant measurement result of an eNB and information of a serving cell;
Step 25a/25b: The eNB triggers a dedicated random access procedure to obtain a TADV TYPE2 and triggers a measurement of an AoA at the physical layer as requested by the E-SMLC;
Step 26: The E-SMLC calculates location information of the UE according to measurement results of the eNB and inputs from other parts;
Step 27: The E-SMLC sends a location result (the location information) to the MME;
Step 28: The MME sends the location result (the location information) to the LCS client, where the LCS client may be the positioned UE itself.
MDT measurements are categorized as follows:
An immediate MDT refers to an MDT measurement and report made in a connected state. A Radio Resource Management (RRM) measurement mechanism is reused, and once a report condition is satisfied, a report is made to an eNB or a Radio Network Controller (RNC) immediately.
A Logged MDT refers to an MDT measurement in an idle state and a report in a subsequent connected state. Once a configured trigger condition is satisfied, a measurement result is obtained and logged and is reported to an eNB or an RNC on a subsequent appropriate occasion.
A configuration and a report of the immediate MDT will be introduced as follows:
The immediate MDT is adopted in a connected state.
The immediate MDT is still based on the existing measurement mechanism, and geographical location information is added thereto. The geographical location information is optional, and a UE is not required by a network to obtain precise geographical location information for the purpose of MDT.
An immediate report is made for the immediate MDT without recording any time information by a UE. All of the time information is determined by an eNB or an RNC from the time when an MDT measurement result is reported by the UE.
In the LTE system, the following bolded section relates to an MDT-related measurement result.
MeasResults ::=SEQUeNBCE { measId  MeasId, measResultPCellSEQUeNBCE {  rsrpResult  RSRP-Range,  rsrqResult  RSRQ-Range }, measResultNeighCellsCHOICE {  measResultListEUTRA  MeasResultListEUTRA,  measResultListUTRA  MeasResultListUTRA,  measResultListGERAN   MeasResultListGERAN,  measResultsCDMA2000   MeasResultsCDMA2000,  ... }   OPTIONAL, ..., [[ measResultForECID-r9 MeasResultForECID-r9OPTIONAL ]], [[ locationInfo-r10 LocationInfo-r10OPTIONAL,  measResultServFreqList-r10  MeasResultServFreqList-r10 OPTIONAL ]]}
A flow of reporting an MDT measurement result, as illustrated in FIG. 5, includes:
A user equipment makes a measurement according to a measurement configuration of a network and reports a result to an eNB or an RNC, and the eNB or the RNC further forwards the MDT measurement results to a Trace Control Entity (TCE) through an Element Management (EM) entity after collecting the MDT measurement results for a period of time. In this flow, the eNB or the RNC is responsible for forwarding a trace record to the TCE.
In summary, all of the existing positioning schemes involve the location server, and most of them have to be assisted by the user equipment. During the MDT procedure, the existing scheme is as follows: the user equipment tries its best to provide location information according to its own condition without additionally obtaining location information for the purpose of MDT, consequently the existing scheme may be limited by the positioning capability of the user equipment.